Ultrasonic wire drawing



' Filed May 26, 1965 Sept. 19,196? 0, FUCHS ETAL 3,342,050

ULTRASONIC WIRE DRAWING 5 Sheets-Sheet 1 FIG.

By K. OLSEN ATTOPNEV Sept. 19, 1967 Filed May 26, 1965 E. O. FUCHS ETALULTRASONIC WIRE DRAWING 3 Sheets Sheet 2 p 19, 1957 E. o. FUCHS ETAL3,342,050

ULTRASONIC WIRE DRAWING 5 Sheets-Sheet 5 Filed May 26, 1965 FIG. 3

DIAMETER (INCHES) 2 m s M 0 5 a -w. w 4 w 0 m b W F O. M M 0 m 0.. o m mw a m o United States Patent 3,342,00 ULTRASONIC WIRE DRAWING Edward 0.Fuchs, Union, Robert F. Jack, Convent Station, and Karl M. Olsen,Madison, N.J., assignors to Bell Telephone Laboratories, Incorporated,New York, N.Y., a corporation of New York Filed May 26, 1965, Ser. No.458,945 11 Claims. (Cl. 72-60) This invention relates to drawing wire orsimilar continuous stock through a die member to reduce the diameter ofthe wire or stock.

The invention is based on the development of a wire drawing techniquecapable of producing long lengths of wire having a surface quality farsuperior to that obtained by normal drawing procedures.

The surface condition of wire is an important factor which must beconsidered in the development of many components designed for use incomplex communications systems as well as many other applications.Improved surface quality is being sought in all wire sizes from heavyconductors to fine wire below 0.0015 inch diameter.

The source of surface imperfections in wire can be divided into twocategories; those present in the starting rod stock, and thoseintroduced by the wire drawing process.

During recent years advances in melting, casting and processingtechniques have led to production of high quality rod stock which isrelatively free of physical defects. Some of the advances are: vacuumcasting, consumable arc and electron beam melting, reduction information of seam, overfills etc. during hot fabrication, and removal ofthe outer surface layer on rod by scalping, centerless grinding orchemical treatment. Preparation of rod stock directly from the moltenstate by continuous casting through rolls is now in the early stages ofcommercial production. Furthermore, the use of high-purity materials hasminimized the presence of metallurgical inhomogeneities such as secondphases and metalloid or oxide inclusions. For example, it is nowpossible to obtain commercial quantities of copper rod with a certifiedpurity of 99.99%. In addition, it has been shown that a large variety ofpure nickel and iron alloys can be made in which no single impurity ispresent in amounts exceeding 0.005% by weight (50 ppm.) Nickel materialshaving this degree of purity are now being made on a commercial scale.

Since high-quality rod stock for drawing can be procured, the remainingmajor source of defects are those introduced by the wire drawingprocess. Some of the common defects are:

1) Longitudinal scoring caused by drawing through worn dies or throughabrasive debris accumulated in the entry area of the die.

(2) Randomly distributed imperfactions produced by embedding of foreignparticles into the wire as it passes over pulleys, capstans and throughdrawing dies.

(3) Voids created when some of the embedded particles become dislodgedfrom the wire surface in drawing to finer sizes.

(4) Transverse chatter and roughness markings due to inadequatefunctioning of the die lubricant.

It is apparent that the cause of these surface imperfections isassociated primarily with pickup of foreign matter from the surroundingenvironment, the drawing machine, and the liquid lubricant. Possibleimprovements in surface finish might be realized by the use ofsuperclean white rooms, spotlessly-clean drawing apparatus,controlled-atmosphere enclosures, elaborate filtering ofcontinuously-circulated lubricants or other similar methods. In manyinstances, these procedures would be costly, impractical and not easilyadaptable to normal Wire drawing processes.

According to the present invention ultrasonic energy is used to agitatethe liquid lubricant in a tank through which the Wire is being pulledover pulleys and drawn through the totally submerged die. With propercavitation intensity the surface of the wire is well-cleaned beforeentering the die. In addition, particles in the liquid bath are kept insuspension and are not deposited on the wire prior to its passagethrough the die. Furthermore, the transmission of ultrasonic energythrough the liquid to the die is intense enough to prevent accumulationof foreign matter in the die cavity.

Ultrasonic energy itself is not new to the wire drawing art. It has beenproposed in several instances for improving wire drawing performance.Typical of such proposals is the teaching in United States Patent2,638,207 issued to R. P. Gutterman on May 12, 1953. The principal ideais to reduce frictional forces by drawing wire through a die which isvibrated by direct metallic connection to a source of ultrasonic power.Experience using this suggestion has encountered the problem ofoverheating of the die, and consequent seizure of the wire in the dieresulting in wire breakage. Even though reduction in friction may berealized in relatively slow-speed drawing of short lengths of Wire, therapid movement of the constricting die surface over the wire continuallyincreases frictional heat until seizure occurs. The dissipation of theultrasonic energy in the form of heat decreases its efficiency and alsolimits the power that can be transmitted to the die. Unfortunately thepoint at which suflicient ultrasonic energy is applied to obtain asignificant benefit coincides with the energy level where overheatingbecomes a problem. For this reason, along with others, the use ofultrasonics in wire drawing apparatus has not achieved commercialacceptance.

According to the present invention ultrasonic energy is used in anentirely different manner in the drawing of wire and similar stock toachieve new and unexpected results. Specifically, large quantities ofwire can be drawn with improved surface quality at percentage reductionsand rates significantly above those obtainable using prior art drawingprocesses.

The invention requires the combined use of ultrasonic energy and a fluidin which the die and the wire being drawn are immersed. This combinationis particularly useful since the fluid acts as a lubricant and coolantfor the die as Well as to introduce the novel ultrasonic effects. Usingthis arrangement the ultrasonic energy is effectively applied to thefluid in close proximity to the die and to the wire prior to its beingdrawn through the die. The consequence of ultrasonically agitating thefluid in this manner is to reduce die friction and die wear and topermit the drawing of long lengths of wire with an unusuallyhigh-quality, smooth, surface finish. All of the reasons for thisimproved drawing behavior are not fully understood. However, it islikely that some of the factors involved are the ultrasonic precleaningof the wire, the continuous cleaning of the entry area of the die by theagitated fluid and the cavitational activity of the fluid at the dieproviding enhanced lubrication.

These and other aspects of the invention may be more fully appreciatedupon considering the following more detailed description of theinvention. In the drawing:

FIG. 1 is a perspective view of an apparatus embodying the principles ofthe invention showing wire-drawing apparatus immersed in an ultrasonictank with the top lid open to permit an overall view;

FIG. 2 is a schematic front-sectional view of the apparatus of FIG. 1showing the transducers in place adjacent to both the wire being drawnand the die;

FIG. 3 is a reduction schedule for copper wire drawn on the apparatus ofFIGS. 1 and 2 showing the reduction in wire diameter per pass for a ninestage (9 dies) reducing operation; and

FIG. 4 is a similar reduction schedule for high-purity aluminum wire.

An apparatus used to demonstrate the principles of the invention isshown in FIGS. 1 and 2. In FIG. 1 a perspective view is shown of thetank, the submerged rolls and die assembly, and the tank lid whichcarries the ultrasonic transducers. The lid is shown in the openposition for a clearer picture of the apparatus.

The tank 10 is a stainless steel container having dimensions of 36inches x inches and an approximate depth of 8 inches. The wire 11 istaken from a spool 12 and threaded over a pay-out pulley 13. After itenters the tank it is fed around driven roll 14 along the length of thetank, around driven roll 15, returning through the first die 16. Thepulleys are free wheels. In this particular apparatus provisions aremade for twelve reduction stages as shown mounted on the die holderplate 17. The wire passes around each end roll and through each die insuccession. After the last pass the Wire loops around the end roll 15,emerges from the tank over free pulley 18 as it is being pulled by themotor-driven capstan 19 and is spooled on a take-up reel 20. The give-upand take-up spooling devices are, in practice, somewhat more elaborateand use servo motors which permit precise control of wire tension.

The stainless steel transducers 21 containing resonant piezoelectriccrystal units are rated at 150 watts and are mounted on the lid 22 ofthe equipment. The ultrasonic generator for this particular unitdelivers approximately 1000 watts so that the six transducers, eachrated at 90% efiicient, deliver approximately 900 watts to the fluid inthe tank. To avoid excessive dissipation of this energy in the fluidprior to reaching the wire it is important to arrange the transducers inclose proximity to the path of the wire and the dies. This can be seenin FIG. 2 which is a schematic front-sectional view of the apparatus ofFIG. 1 showing the top lid 22 in place. The separation should not exceed12 inches and is preferably less than 6 inches. For the apparatusdescribed herein the fluid space between the wire 10 and the surface ofthe transducer 21 was less than one inch and the return or lower passwas approximately 3 /2 inches from the transducer surface. Obviously itmakes little difference whether the transducers are top, bottom or sidemounted with respect to the wire and die or dies.

A survey was made of the capability of this new machine for producingfine wires of a variety of metals and alloys. All of the starting wirewas chemically cleaned. Except as noted, all the wire was drawn throughan elevendie setup in the multi-die holder 17 at a speed of 150 to 200feet per minute under an ultrasonically agitated lubricant solutionconsisting of 0.1 percent by volume of vegetable oil compound indistilled water. The average reduction in area through each die wasapproximately 15 percent. The results of the survey are as follows:

length of 0.0007 inch diameter wire (#53 B & S).

OFHC copper wire was drawn from 0.015 inch to Copper 0.0028 inchdiameter at 1000 feet per minute using average reductions of 30% perdie. The reduction schedule for this drawing operation is given in FIG.3. The ordinate is plotted as percent reduction vs. wire diameter on theabscissa. Each pass (reduction stage) is designated by a triangular plotpoint. As can be seen, only nine dies were used for drawing this wire ascompared with the fourteen dies required by conventional (B & S) gaugereductions schedule. (Approximately 20% reduction per die.) Examinationof the dies after this heavy-reduction, highspeed drawing showed noaccumulation of particles in the entry area of the dies.

(2) High-purity aluminum (99.99+%) Perhaps the most startlingdemonstration of the effectiveness of employing ultrasonically agitatedliquid lubricants in wire drawing was the success achieved in drawingvery soft, pure, aluminum. No difficulty was encountered in producing a5000 foot continuous length of 0.005 inch diameter wire by drawing 0.030inch diameter wire through two sets of eleven dies. A portion of thiswire was drawn through another set of eleven dies to produce 1000 feetof 0.0028 inch diameter wire. During the drawing operation it wasobserved that the ultrasonic cleaning action was causing evolution of acloud of fine particles from the surface of the wire located in thesections between the dies. The same evolution was observed duringsubsequent drawing through the following sets of dies. When the drawingoperation was completed and the ultrasonic agitation was stopped, theparticles (which are probably aluminum oxide) remained in suspension andcould not be removed by the available filtering equipment. However, noevidence of the presence of these particles was found in the entry areasof the dies after drawing. The ability of the ultrasonic action to cleanthe surface and keep the particles out of the die was undoubtedly amajor factor in overcoming the usual difficulty of drawing pure aluminumto fine wire.

The reduction schedule for drawing the pure aluminum wire is shown inFIG. 4. The coordinates are the same as in FIG. 3. Availableconventional diamond dies were used whose bore sizes decreased uniformlyin increments of 0.002 inch, 0.001 inch, etc. This accounts for thesteplike character of the reduction schedule curve. The averagereduction per die was approximately 12 percent and the processing of the0.0028 inch diameter wire required thirty-three reduction stages(achieved by three passes of the wire through the 11 die setup). It isvery possible that fewer dies would be needed if appropriate matchedsets of short bearing dies were used.

High nickel content alloys All of these alloys were drawn from 0.020inch to 0.001 inch diameter with no difliculty. About 1000 feet of thehard Ni-Cr-Al-Cu alloy was drawn from .001 inch to 0.0007 inch diameterusing a set of nine dies and an average of 10% reduction per die.

Fine particle evolution similar to that obtained in drawing aluminum wasobserved in drawing the Ni-Cr- Al-Cu alloy. In drawing the high-puritynickel-chromium alloy, particles settled out quickly to form a blacksmudge on the bottom of the tank when the ultrasonic energy was shut offat the end of the processing. This smudge was found to be mainly nickeloxide. No significant accumulation of these particles was found in theentry area of the dies after drawing any of the high nickel contentalloys.

To date a variety of materials ranging from very soft aluminum to hardnickel alloys have been drawn into fine wire using the new multi-diemachine. Dimensional uniformity along the length of the copper,aluminum, and Ni-Cr-Al-Cu wire was determined by calculations derivedfrom electrical resistance measurements. The measurements were made onseveral samples taken from locations corresponding to the start,midpoint, and end of the wire drawing. The maximum variation in areaalong the length was found to be i0.2%. Such a slight variation for 1000feet of 0.0028 inch diameter pure aluminum wire shows that-this softmaterial is not being stretched after pulling through the last die.

The foregoing examples show that in addition to providing a means forimproving the surface condition of wire, the use of ultrasonicallyagitated liquid lubricants in wet wire drawing processing enhances thefeasibility of drawing wire to fine sizes. The high frequency agitationof the liquid undoubtedly lowers the frictional resistance associatedwith the drawing operation. A large part of the decrease in friction isdue to the ability of the ultrasonic action to clean the wire surface,to keep foreign particles suspended in the liquid, and to preventaccumulation of debris in the die cavity.

It is felt that other beneficial actions must also be operative toaccount for the success achieved in the drawing operations describedabove. For instance, it is difiicult to believe that control ofcleanliness alone would enable long lengths of soft aluminum wire to belaced around driven rolls 2 /2 feet apart and drawn through eleven diesat a speed of 100 feet per minute, especially when it is realized thatthe breaking load of the aluminum wire decreases from 350 to 100 gramsas a result of the reduction from 0.005 inch to 0.0028 inch diameter.There is some evidence that the cavitational energy transmitted by theliquid exerts enough penetrating action to force the liquid through thedie along with the wire thereby providing a hydrodynamic lubricatingeffect. The strong penetration eflect may also maintain a liquid filmunder the area of contact between the wire and the driven rolls whichprovides a cushioning effect and prevents erratic slippage of the wirepassing over the rolls during the drawing operation.

It should be appreciated that an appropriate amount of ultrasonic energymust be applied to the fluid in the vicinity of the wire and the die ordies to obtain the results discussed above. Accordingly, for thepurposes of this invention ultrasonic energy at a power density of atleast 1 watt/in. of transducer area must be delivered to the fluidadjacent the die area and the wire prior to entry into the die.Especially good results are obtained with a power density of at least2.5 watts/m It is preferred that this power density be applied to theliquid over a length of twelve inches encompassing the die region andthe wire path entering the die. This prescribed power density isregarded as a minimum for high-speed wire drawing, e.g., one thousand toseveral thousand feet per minute. Consequently these limitations on theultrasonic energy are valid for any conventional wire drawing rate. Ifthe rate is extended beyond normally used rates the power density may beincreased proportionately or longer exposure lengths used. Slower speedspresent no difliculty as the only possible critical parameter is themini inumhuseful exposure time for a given increment of wire engt Theultrasonic frequency may vary from 20 kc. to 400 kc. The transducersused in the equipment described in this specification operated at 25 kc.

Various modifications in the arrangement described here may be madewithin the scope of the invention. For instance, the fluid compositionmay be varied. Trichloroethylene is useful for its solvent capabilitiesand its physical properties may permit useful cavitation at slightlylower power levels. Kerosene, benzene, alcohol, acetone, etc., are otheralternative fluids. Obviously, since the hydrodynamic characteristics ofthe fluid are as important as its chemical behavior, a wide latitude inthe selection of the fluid is possible. In many instances the type offluid used will be dependent upon the nature of the wire being drawn.Water is economic, relatively inert, and has been found to beparticularly effective for this application. Lubricant additives otherthan the Vegetable oil used here may be employed with the water.

While it is convenient to operate the equipment at room temperature thefluid may be heated if desired to increase the efficiency of theultrasonic agitation. Temperatures around 60 C. are especially good forwater.

The apparatus can be constructed in various designs. For instance, agiven tank or portion of a tank may contain several dies of the samesize and a plurality of continuous filaments may be treatedsimultaneously, side by side, passing through several die stations toachieve the desired reduction. Several similar alternative arrangementsmay also be foreseen.

While the invention is particularly applicable to drawing wire for sizereduction, it should be understood that it is also useful in connectionwith the size reducing of other continuous stock where the continuousfilament is drawn through a die. Such materials as rods, tubes and thinsheets or tapes are in this category. The considerations and resultsdiscussed herein apply to wire or other continuous stock of any ordinarydimensions.

Various other modifications and deviations which basically rely on theteachings through which this invention has advanced the art are properlyconsidered Within the spirit and scope of this invention.

What is claimed is:

1. An apparatus for drawing continuous stock through a die comprising afluid-tight, a die mounted below the rim of the tank adapted to becompletely immersed with fluid in the tank, means for drawing thecontinuous stock through the die, ultrasonic means adapted for applyingultrasonic energy to a fluid contained in the tank said ultrasonic meansdisposed in a position to deliver ultrasonic energy at a power densityof at least 1 watt/in. to the region of the fluid containing the die anda twelve inch length defined by the path of the continuous stock justprior to entering the die, the said ultrasonic means in said regionspaced at less than twelve inches from the said die and continuous stockpath.

2. A method for drawing continuous stock through a size reducing diewhich comprises drawing the continuous stock through a die substantiallycompletely immersed in a fluid while applying ultrasonic energy to thefluid at a power density of at least 1 watt/in. in the region of the dieand over at least a twelve inch length of the path of the continuousstock just prior to entering the die, the effective power density ofsaid ultrasonic energy occurring within less than twelve inches of thedie and the continuous stock.

3. The method of claim 2 wherein the fluid comprises a member selectedfrom the group consisting of water, trichloroethylene, kerosene,alcohol, acetone and benzene.

4. The method of claim 3 wherein the fluid comprises water.

5. The method of claim 2 wherein the continuous stock is wire.

6. The method of claim 5 wherein the wire is copper.

7. The method of claim 5 wherein the wire is aluminum.

8. The method of claim 5 wherein the Wire is a nickel alloy.

9. The method of claim 2 is at least 2.5 watts/m 10. An apparatus fordrawing wire to reduce its diameter comprising a fluid-tight tank, aplurality ofdies mounted within said tank below the fluidsurface-definin-g level of the tank, wire handling means associated withsaid tank including roller means disposed within said tank below saidsurface-defining level for passing a continuous wire through anultrasonic treatment portion Within said tank and directly thereafterthrough said dies,

wherein the power density said ultrasonic treatment portion having alength of at least twelve inches as measured along the wire path definedby the wire handling means and consisting of at least one ultrasonictransducer mounted on said tank and capable of delivering ultrasonicenergy at a power level of at least 1 watt/m the said transducer havingits effective surface extending over the entire ultrasonic treatmentportion of the tank and spaced within six inches of the said wire path.

11. The apparatus of claim 10 wherein the said wire handling means isarranged to pass at least one Wire se- 3 quen-tially through at leastsome of said dies certain of which have varying size.

References Cited UNITED STATES PATENTS 2,638,207 5/1953 Gutterman 72-284CHARLES W. LANHAM, Primary Examiner.

0 H. D. HOINKES, Assistant Examiner.

1. AN APPARATUS FOR DRAWING CONTINUOUS STOCK THROUGH A DIE COMPRISING AFLUID-TIGHT, A DIE MOUNTED BELOW THE RIM OF THE TANK ADAPTED TO BECOMPLETELY IMMERSED WITH FLUID IN THE TANK, MEANS FOR DRAWING THECONTINUOUS STOCK THROUGH THE DIE, ULTRASONIC MEANS ADAPTED FOR APPLYINGULTRASONIC ENERGY TO A FLUID CONTAINED IN THE TANK SAID ULTRASONIC MEANSDISPOSED IN A POSITION TO DELIVER ULTRASONIC ENERGY AT A POWER DENSITYOF AT LEAST 1 WATT/IN.2 TO THE REGION OF THE FLUID CONTAINING THE DIEAND A TWELVE INCH LENGTH DEFINED BY THE PATH OF THE CONTINUOUS STOCKJUST PRIOR TO ENTERING THE DIE, THE SAID ULTRASONIC MEANS IN SAID REGIONSPACED AT LESS THAN TWELVE INCHES FROM THE SAID DIE AND CONTINUOUS STOCKPATH.